Does a Christmas Tree make a room warmer

On Radio 1 there was a discussion on whether a christmas tree would make a room warmer, or whether this effect was negligible. Here are my thoughts:

There are a number of thermal effects that the tree will have on the room,

1. The Christmas tree is a fresh tree so will be predominantly water ( I hope that the tree will be fed with water regularly to help it's needle retention) Water has a higher heat capacity (the amount of energy that it needs to heat it up) than the air it has displaced in the room. To calculate the difference in energy in joules needed to heat up the room do the following equation. Mass (weight) of tree in grams * thermal heat capacity of tree (approx 3.68 J/g.K) assuming it is 80% water and 20% wood) then subtract the mass of air it displaces, or mass of air it displaces x 1.0035 (J/g.k). This will end up with a very small number, as the effect is negligible. This number will be useful as it will tell you how much extra energy you would use to heat up the tree, per degree Kelvin the temperature raised. Basically you will spend more on your heating bill to heat up the water in the tree.

2. You will also increase the internal relative humidity of the environment as the tree loses water to the room through it's leaves and through evaporation from the pot that you should keep topping up. Humid air also takes more energy to heat up as it contains more water. The calculation is much the same as above.

3. As the thermal mass in the room will increase and the relative humidity of the room is higher, your heating will take longer to heat the room and conversely the room will take longer to cool down.

4. There is also the negligible effect that there is less air in the room, as the air will be displaced by the tree. This will lessen ventilation heat losses from the house, as there is proportionally less heated air in the house. Air will escape at an identical rate, but the overall warmed air in the house will be less.

In total the water in the tree will make your house warmer, but only as it will force the heating on a thermostat to work longer. This is because heat is not introduced instantaneously by magic into the house by the tree. If left for two years to season, you could say that it is energy as you could then burn the tree inside the house, but that's not very christmassy is it? The tree will slightly reduce the thermal losses from the house through reducing air mass that can lose heat.

Now the lights, have we considered the lights. Well although not actually the tree, the lights are a big part of the tree and could potentially introduce warmth into the room by their inefficient operation. Most of the energy an incandescant light bulb (Edison bulb) uses is turned into heat, making it a very good heat emitter. So if you had 100, 10W bulbs on your tree, roughly 90% of that power would be turned into heat or 900W, a good sized radiator. If the lights on the tree were LEDs, however, 99% of the energy going into the room would be light energy and 1% would be heat energy. So again if you had 100 10W LED bulbs, it would be much brighter and the LED's would emit 1W of heat, which is almost not worth bothering about in the average sitting room.

Now thermal comfort is not an objective thing and is also based on human perception, so,

1. Having the tree in the room might make the room feel nicer, so you perceive it to be warmer as nicer environments generally are perceived to be warmer, even though they are not warmer.

2. The overall radiative heat balance might be more equal, if the tree is in a corner, then that might be on an external wall and the tree has blocked lesser radiated heat. This is the opposite of the phenomenon of the warmth that you feel on your skin when the sun shines on it. It is not irradiating coolth, just radiating less heat. If your body feels the same irradiation all around it, it feels more comfortable.

3. With more water in the air, and the increased humidity, this can make you feel things are warmer, even though they are not.

Not very Christmassy I know, but a Christmas Article non the less.